192 



E. A. STEPHENSON 



case did there appear, under the microscope, to be any change. 

 No gelatinous silica separated from the solutions after long standing. 

 Group IV: Potassium fluoride solutions on feldspars and horn- 

 blende. — Fluorine has long been looked upon as one of nature's 

 important mineralizers ; r it occurs in small quantities in the emana- 

 tions from Kilauea, 2 is abundant as fluorite in metalliferous veins, is 

 a constituent of many minerals such as apatite, amblygonite, lepi- 

 dolite, topaz, and cryolite, and is considered by Spurr 3 an essential 

 constituent of muscovite. Table IV shows the experiments con- 



TABLE IV 



*This salt contained a small amount of tha acid salt HKF 2 . 



ducted with potassium fluoride. In experiments Nos. 14, 15, 16, 

 and 17 the feldspars showed no change other than a possible slight 

 etching. In No. 16 there appeared some minute bacteria-like rods 

 that were not further identifiable. In No. 18 the hornblende was 

 vigorously attacked. The product is an amorphous brown mass 

 resembling limonite and consisting of hydrated iron oxide together 

 with grains of partially altered mineral. Some of these grains are 

 bleached to isotropic transparency, others have a rim of isotropic 

 matter surrounding ellipsoidal grains in the interior. No gelatinous 

 precipitate appeared in the decanted solution on standing in paraffin 

 lined bottles for several months. In No. 19 the tube burst and the 

 mineral appeared unchanged. 



Group V: Mixtures of carbonate and fluoride solutions on feldspars 

 and hornblende. — Since the feldspars were not visibly attacked by 

 the fluoride solutions but had been attacked by the alkaline carbo- 



1 See especially C. Doelter, AUgcm. chcm. Min., p. 207, and W. Bruhns, Neues 

 Jahrb. Min. Gcol, II (1889), p. 26. 



3 A. L. Day and E. S. Shepherd, Bull. Geol. Soc. Am., XXIV, 592. 

 3 J. E. Spurr, Professional Paper 42, U.S. Gcol. Survey, p. 233. 



